SCARA type robots are generally used to take out semiconductor wafers or liquid crystal substrates from carriage cassettes and hand them over to various processing devices, and to subsequently transfer them to the ensuing process, e.g. to taken them back to the carriage cassettes after the processes by the processing devices. The SCARA type is an abbreviation derived from initial letters of Selective Compliance Assembly Robot Arm. In SCARA type robots, the bending and stretching of the arm unit as well as the horizontal movement of the fingers are realized by turning of each arm in the horizontal plane. SCARA type robots are often used in an anti-dust environment. In the initial phase, a robot comprising one arm unit, linked to the body, to linearly move a finger was used.
Later, in order to improve the efficiency of transferring wafers etc., for example, as shown in Japanese Patent No. 273941, another mode of SCARA type robot has been developed, wherein two arm units are installed to the pivotable body, and which carries wafers and the like twice as efficiently by alternately and linearly moving two fingers in the same direction in both arm units.
In addition, in Japanese Unexamined Patent Application Publication No. H11-163090, as shown in FIG. 14, yet another mode of SCARA robot has been suggested, whose arm unit 14, although single, comprises three arms, and wherein two finger portions 16 located at a tip portion of the arm unit, arranged at an angle of 120 degrees in-between, are fixed to one wrist portion 15. By this, operations such as an operation of causing one finger portion 16 to transfer the unprocessed wafer while causing the other finger portion to receive the fabricated and processed wafer has been made possible, and accordingly the efficiency of the transferring is improved. In addition, since the arm unit 14 comprises the three arms, there is an advantage that the finger portion 16 is caused to reach farther.
However, the former of the foregoing conventional SCARA type robots is constructed in a way that the two arm units cause the two fingers to move linearly in the same direction. For this reason, when carrying the wafer to, and from, target instruments such as a wafer processing instrument and a wafer cassette, the robot has to be located in front of the target instrument. When target instruments such as a wafer cassette and a processing instrument are arranged in a line in the lateral direction, the robot itself has to be moved in the lateral direction by providing a track along the line of these instruments. When the track was constructed, the construction entailed costs, but also required the area of a place where the robot can be moved and operated to be larger. Accordingly, the area used for this inside the expensive clean room was required to be larger, and this was what was not preferable.
In this regard, as in the case of the latter conventional example shown in FIG. 14, in order to reduce costs and improve the efficiency of the transferring, an SCARA type robot having a wrist portion to which the two fingers are fixed in the tip portion of the single arm unit has been suggested. In such a conventional robot, the combination of the pivotable wrist portion and the arm unit capable of linearly moving the wrist portion has made it possible to freely carry the wafer to, or from, the target instrument diagonally in the front thereof, without moving the robot itself in the lateral direction (in the x axis direction). However, since the two fingers are integrally installed in the single wrist portion, an area where the wrist portion is turned while holding two wafers is required in front of the target instrument. In addition, in the case that an entrance towards the target instrument is narrow, there are disadvantages, for example, such as a disadvantage that the other finger hiders the delivering of the wafer to the target instrument.
Further, in the latter conventional example, a heavy motor which drives to turn the wrist portion to which the two fingers are installed is arranged in the tip portion of the arm unit. In addition, the arm unit is long since the arm unit comprises the three arms. Consequently, each arm needs to be made thick due to the necessity of maintaining the rigidity, the force of inertia while moving the arm unit is large, and a larger power for driving the arm unit is necessary. In addition, it is difficult to precisely conduct positioning when the arm unit is stopped.
Furthermore, in the latter conventional example, there is no stopper to limit pivotal angles of the arm unit and the wrist portion. It is likely, therefore, that electric wiring to the motor and sensor installed to the wrist portion, vacuum piping to the suction holes of the finger tip and the like may be excessively wrenched and twisted off. If the turning portions are intended to be provided with a known stopper comprising a stopper pin and a stop face, the turning angles are limited to only less than 360 degrees (one turn). Therefore, a disadvantage would arise that operations which require significantly different directions, for example, such as handing over in front of the robot and handing over in the rear of the robot cannot be conducted continuously.